Coordination and response

• Mammalian Nervous System


  The human nervous system consists of the central nervous system (CNS) - the brain and the spinal cord, and the peripheral nervous system (PNS) - all of the nerves in the body
• Functions of the Mammalian Nervous System

  • Makes sense of our surroundings and respond to them
  • Coordinates and regulates body functions
• Nerve impulses


  Electrical signals that pass along nerve cells known as neurones
• Nerve


  A bundle of neurones
• Components of the Nervous System

  • Central Nervous System (CNS)
  • Peripheral Nervous System (PNS)
  • Nerves
• Central Nervous System (CNS)


  • Brain
  • Spinal Cord
• Peripheral Nervous System (PNS)


  • All nerves in the body
• Neurone


  • Long fibre (axon)
  • Axon insulated by fatty sheath with small uninsulated sections (nodes)
  • Cell body with many extensions (dendrites)
• Types of Neurones


  • Sensory neurones
  • Relay neurones
  • Motor neurones
• Sensory neurones


  Carry impulses from sense organs to the CNS (brain or spinal cord)
• Relay neurones


  Found inside the CNS and connect sensory and motor neurones
• Motor neurones


  Carry impulses from the CNS to effectors (muscles or glands)
• Voluntary response


  A response where you make a conscious decision to carry out a particular action, therefore it starts with your brain
• Involuntary (or reflex) response

  A response that does not involve the brain as the coordinator of the reaction and you are not aware you have completed it until after you have carried it out
• Involuntary actions


  • Usually ones which are essential to basic survival and are rapid, whereas voluntary responses often take longer as we consider what the consequences might be before doing it
• Reflex response


  An automatic and rapid response to a stimulus such as touching something sharp or hot, as it does not involve the brain, a reflex response is quicker than any other type of nervous response
• Reflex arc


  1. The pin (the stimulus) is detected by a pain/pressure/touch receptor in the skin

  2. Sensory neurone sends electrical impulses to the spinal cord (the coordinator)

  3. Electrical impulse is passed on to relay neurone in the spinal cord

  4. Relay neurone connects to motor neurone and passes the impulse on

  5. Motor neurone carries impulse to a muscle in the leg (the effector)

  6. The muscle will contract and pull the foot up and away from the sharp object (the response)
• Components of the reflex arc

  • Stimulus
  • Receptor
  • Sensory neurone
  • Relay neurone
  • Motor neurone
  • Effector
  • Response
• Synapse


  The junction between two neurones where nerve impulses can transmit across and be directed along the appropriate route
• Synapses allow junctions between neurones so are important in the nervous system being a connected network of neurones</b>
• Nerve impulses can transmit across synapses and be directed along the appropriate route by them eg. to the correct part of the brain
• Reflex actions are automatic, fast, and protective
• Neurones


  Never touch each other, the junctions (gaps) in between them are called synapses
• Impulse transmission at a synapse

  1. Electrical impulse travels along first axon

  2. Triggers nerve-ending of presynaptic neurone to release neurotransmitters

  3. Neurotransmitters diffuse across synaptic gap and bind to receptors on postsynaptic membrane

  4. Stimulates second neurone to generate electrical impulse

  5. Neurotransmitters destroyed to prevent continued stimulation
• Synapses


  • Ensure impulses only travel in one direction, avoiding confusion in nervous system
• Synapses are the only part of the nervous system where messages are chemical rather than electrical, allowing drugs to act on the nervous system
• Receptors


  Groups of specialised cells that detect changes in the environment and stimulate electrical impulses
• Sense organs and what they are sensitive to

  • Skin - pressure, heat, cold, pain
  • Tongue - chemicals in food/drink
  • Nose - chemicals in air
  • Ear - sound, movement
  • Eye - light
• Sensory perception process


  1. Receptor cell in sense organ stimulated

  2. Generates electrical impulse

  3. Passed to sensory neurone

  4. Impulse carried to central nervous system

  5. Response decided

  6. Impulse passed to motor neurone

  7. Motor neurone carries impulse to effector
• Eye


  Sense organ containing receptor cells sensitive to light (rods) and colour (cones)
• Parts of the eye and their functions

  • Cornea - refracts light
  • Iris - controls light entering pupil
  • Lens - focuses light onto retina
  • Retina - contains light receptor cells
  • Optic nerve - carries impulses to brain
  • Pupil - allows light to enter eye
• Blind spot


  Part of retina where optic nerve joins, no light receptor cells so no image detected, brain 'fills in' the gap
• Pupil reflex


  1. Pupil dilates in dim light to allow more light

  2. Pupil constricts in bright light to prevent retina damage
• Pupil reflex


  In dim light, the pupil dilates (becomes larger) to allow more light to enter the eye to improve vision. In bright light, the pupil constricts (gets smaller) to allow less light to enter the eye to protect the retina from damage.
• Pupil reflex


  1. Radial muscles contract

  2. Circular muscles relax

  3. Pupil dilates (more light enters eye)

  4. Radial muscles relax

  5. Circular muscles contract

  6. Pupil constricts (less light enters eye)
• Dim light


  Pupil dilates (more light enters eye)
• Bright light


  Pupil constricts (less light enters eye)
• Responding to changes in light intensity

  • Radial muscles
  • Circular muscles
  • Pupil size
  • Amount of light entering
• Accommodation


  The function of the eye in focusing on near and distant objects
• Accommodation for near object

  1. Ciliary muscles contract

  2. Suspensory ligaments slacken

  3. Lens becomes fatter

  4. Light is refracted more